1. Field of the Invention
The present invention relates to a light-reflecting film that has a layer formed by fixing a cholesteric liquid crystal phase and that reflects infrared light, and a production method thereof.
2. Description of the Related Art
With the recent increase of concern over and interest in environment or energy, energy-saving industrial products have been increasingly demanded. For example, glass and films have been required which could effectively shield glass windows of houses or vehicles from heat, that is, effectively reduce the thermal load due to sunlight. In order to reduce the thermal load due to sunlight, it is necessary to prevent the transmission of some solar rays in the visible light region or the infrared light region in a solar light spectrum. Particularly, from the viewpoint of safety, high transmittance in the visible light region and heat-shielding performance are actively required for vehicle windows and the reflectance of sunlight tends to be regulated in some countries.
Multi-layered glass coated with a special metal film blocking heat radiation, which is called low-E double glazing, is frequently used as echo-glass having high heat-insulating performance or high heat-shielding performance. The special metal film can be produced by laminating plural layers, for example, by the use of a vacuum film-forming method. The coating of the special metal film produced by the use of the vacuum film-forming method is very excellent in reflection performance, but the vacuum process is low in productivity, whereby the production cost thereof is high. When a metal film is used, there is a problem in that electromagnetic waves are also shielded to cause radio interference when using mobile phones or the like. Furthermore, when a metal film is used for vehicles, use of ETC system may be prevented. High transmittance of visible rays is required as well as the radio interference for vehicle windows in view of safety.
On the other hand, a method using a cholesteric liquid crystal phase has been suggested. For example, a laminated optical film in which reflective circularly-polarizing films disposed to transmit circularly-polarized light having the same direction are formed on both surfaces of a cholesteric liquid crystal phase is disclosed in JP4109914B.
An infrared light reflecting article having a cholesteric liquid crystal phase is disclosed in JP2009-514022A. A configuration in which plural cholesteric liquid crystal phase layers are laminated to efficiently reflect light in the visible light region, which is used for a liquid crystal display, is disclosed in JP3500127B.
In laminating plural cholesteric liquid crystal phase layers, for example, a method of drying, heat-orienting, and UV-curing of a coating film containing a cholesteric liquid crystal material and repeating the above steps to laminate a cholesteric liquid crystal phase layer by layer on the previously formed cholesteric liquid crystal phase is used. Regarding the method of curing a cholesteric liquid crystal phase, a method of applying UV rays to a polymerizable liquid crystal is generally used, for example, as disclosed in JP4008358B. JP4008358B discloses a method of producing a cholesteric liquid crystal film of which the reflection wavelength band is wide by adjusting the illumination intensity in a predetermined range. JP3745221B discloses a method of producing a polarizer in which the wavelength region is continuous by setting the rotation directions of liquid crystal molecules in each of cholecteric liquid crystal phases to be identical at the time of laminating the cholesteric liquid crystal phases.
JP3903101B discloses a method of diluting a starting solution by in-line mixing of an additive to the starting solution so as to prevent coating streaks. JP2003-41015A discloses a method of mixing an additive by in-line mixing and stably applying an unstable starting solution.